Planar illumination device and liquid crystal display device using the same

Abstract

A thin planar illumination device with a high light utilization efficiency is provided. In a planar illumination device 10 , light source sections 15, 16, 17 and 18 each radiates laser light. The light guide members 19 and 20 polarize, by total reflection, light incident from side surfaces 19 b and 20 b on two opposite sides thereof, so as to be radiated from incident surfaces 19 a and 20 a , respectively. In a light guide plate 21 , the light is incident from side surfaces beside the respective light guide members 19 and 20 so as to radiate irradiation light 24 from main surfaces 21 a and 21 b . The main surface of the light guide plate 21 is formed by a plurality of inclined surfaces, each being gradually thinned from the edge surfaces on two sides thereof toward a center thereof.

1. A planar illumination device comprising:
 a linear light source section for radiating linear laser light; and 
 a light guide plate for causing the linear laser light to be incident from edge surfaces on two opposite sides thereof so as to be radiated from one main surface, wherein 
 the main surface of the light guide plate is formed by a plurality of inclined surfaces, and 
 the light guide plate is formed so as to be gradually thinned toward a center thereof. 
 
     
     
       2. The planar illumination device according to  claim 1 , wherein
 a thickness of a central portion of the light guide plate is thinner than that of each of the edge surfaces on two sides of the light guide plate. 
 
     
     
       3. The planar illumination device according to  claim 1 , wherein
 the light guide plate has a deflection member for deflecting light incident on a bottom surface, opposite to the main surface, of the light guide plate toward the main surface, and 
 at least one of the plurality of inclined surfaces is formed such that if the one of the inclined surfaces is hypothetically extended, the extended inclined surface would intersect with a portion of the bottom surface. 
 
     
     
       4. The planar illumination device according to  claim 1 , wherein
 the main surface of the light guide plate is formed by the two inclined surfaces which are inclined from the edge surfaces on two sides thereof toward the center thereof, and 
 the light guide plate is formed such that the main surface forms a concave shape. 
 
     
     
       5. The planar illumination device according to  claim 1 , wherein
 the main surface of the light guide plate is formed by the two inclined surfaces which are inclined from the respective edge surfaces on two sides thereof toward the center thereof and one flat surface joined to the two inclined surfaces, and 
 the light guide plate is formed such that the main surface forms a concave shape. 
 
     
     
       6. The planar illumination device according to  claim 1  further comprising a prism sheet for adjusting a radiation angle distribution of light to be radiated from the light guide plate, wherein
 the prism sheet is disposed along the inclined surfaces of the light guide plate. 
 
     
     
       7. The planar illumination device according to  claim 1 , wherein
 a diffusion plate or a lenticular lens is disposed on a side of the main surface of the light guide plate. 
 
     
     
       8. The planar illumination device according to  claim 7 , wherein
 a fine periodical structure is formed on the inclined surfaces of the light guide plate. 
 
     
     
       9. The planar illumination device according to  claim 7 , wherein
 a space between the inclined surfaces of the light guide plate and the diffusion plate or the lenticular lens is sealed. 
 
     
     
       10. The planar illumination device according to  claim 1 , wherein
 the main surface of the light guide plate is formed by the four inclined surfaces disposed in series between the edge surfaces on two sides thereof, and 
 the light guide plate is formed such that two central inclined surfaces among the four inclined surfaces form a convex V-shape. 
 
     
     
       11. The planar illumination device according to  claim 1 , wherein
 the main surface of the light guide plate is formed by the plurality of inclined surfaces, each being gradually thinned toward the center thereof and a plurality of incident surfaces, each being disposed between the inclined surfaces, and 
 the plurality of incident surfaces of the light guide plate are formed such that nearly parallel light radiated from the edge surfaces on two sides thereof is incident on the incident surfaces. 
 
     
     
       12. The planar illumination device according to  claim 1 , wherein
 the light guide plate includes minute diffusion particles in the interior thereof. 
 
     
     
       13. The planar illumination device according to  claim 1 , wherein
 the linear light source section is formed so as to radiate light nearly parallel to the main surface of the light guide plate toward the edge surfaces on two sides of the light guide plate, and 
 in the light guide plate, a large number of deflection ridges are formed on a bottom surface opposite to the main surface so as to deflect, by total reflection, the light incident from the linear light source section. 
 
     
     
       14. The planar illumination device according to  claim 13 , wherein
 the linear light source section is formed such that the nearly parallel light is radiated so as to be polarized horizontally or perpendicularly to the inclined surfaces respectively adjacent to the edge surfaces on two sides of the light guide plate, and 
 the light guide plate is formed such that the nearly parallel light is incident from the linear source section perpendicularly to the edge surfaces on two sides of the light guide plate, and 
 the deflection ridges are formed so as to be parallel to the edge surfaces on two sides of the light guide plate. 
 
     
     
       15. The planar illumination device according to  claim 13 , wherein
 the linear light source section includes: 
 a laser light source for radiating divergent light; 
 a collimate component for converting the divergent light radiated from the laser light source into the nearly parallel light; and 
 a rod-shaped light guide member for causing the light radiated from the collimate component to be incident from edge surfaces so as to be radiated from a side surface. 
 
     
     
       16. The planar illumination device according to  claim 13 , wherein
 the linear light source section includes: 
 a laser light source for radiating divergent light; 
 a collimate component for converting the divergent light radiated from the laser light source into the nearly parallel light; and 
 a polygon mirror for deflecting and scanning the light radiated from the collimate component. 
 
     
     
       17. The planar illumination device according to  claim 13 , wherein
 the linear light source section includes: 
 a laser light source for radiating divergent light; 
 a collimate component for converting the divergent light radiated from the laser light source into the nearly parallel light; and 
 a one-dimensional diffusion component for diffusing the light radiated from the collimate component in a one-dimensional direction by deflection, diffraction or dispersion. 
 
     
     
       18. The planar illumination device according to  claim 13 , wherein
 the light guide plate is formed such that each of the deflection ridges has a curved surface and a tangent of the curved surface is inclined at 30 to 60 degrees with respect to the main surface. 
 
     
     
       19. The planar illumination device according to  claim 1 , wherein
 the light guide plate is formed by injection molding and a gate is provided at the thinnest portion of a side surface orthogonal to each of the edge surfaces on two sides thereof. 
 
     
     
       20. The planar illumination device according to  claim 1 , wherein
 the linear light source section is disposed along longitudinal side surfaces of the light guide plate. 
 
     
     
       21. A planar illumination device comprising:
 a laser light source for radiating laser light; 
 a rod-shaped light guide member for causing the laser light to be incident from edge surfaces on two opposites sides thereof so as to be radiated from a side surface; and 
 a light guide plate for causing the light radiated from the light guide member to be incident from an at least one edge surface so as to be radiated from one main surface, wherein 
 the light guide member is formed so as to have a rectangular cross-section parallel to each of the edge surfaces on two sides thereof, 
 the side surface, of the light guide member, from which the light is radiated is formed by a plurality of inclined surfaces, and 
 the light guide member is formed so as to be gradually thinned toward a center thereof. 
 
     
     
       22. The planar illumination device according to  claim 21 , wherein
 the side surface, of the light guide member, from which the light is radiated is formed by the two inclined surfaces which are inclined from the respective edge surfaces on two sides thereof toward a center thereof, and 
 the light guide member is formed such that the side surface forms a concave shape. 
 
     
     
       23. The planar illumination device according to  claim 21 , wherein
 the side surface, of the light guide member, from which the light is radiated is formed by the two inclined surfaces which are inclined from the edge surfaces on two sides thereof toward a center thereof and one flat surface joined to the two inclined surfaces, and 
 the light guide member is formed such that the side surface forms a concave shape. 
 
     
     
       24. The planar illumination device according to  claim 21 , wherein
 the side surface, of the light guide member, from which the light is radiated is formed by the four inclined surfaces disposed in series between the edge surfaces on two sides thereof, and 
 the light guide member is formed such that two central inclined surfaces among the four inclined surfaces form a convex V-shape. 
 
     
     
       25. A liquid crystal device comprising:
 a liquid display panel; and 
 a backlight illumination device for illuminating the liquid display panel from a side of a bottom surface thereof, wherein 
 the planar illumination device according to  claim 1  is used as the backlight illumination device.